The present invention concerns a process for the production of an improved phenolic resin composite foam.
The phenolic resin foams are superior in heat-resisting properties, such as flame resistance and smoke resistance, to other plastic foams. Phenolic foams are light in weight and low in thermal conductivity. Because of these properties, phenolic foam is used in a great variety of heat insulating applications, but is limited to other application areas because it is poor in compressive strength, flexibility, adhesion to metals and its corrosive nature to metals.
There is disclosed in, for example, Japanese Patent Publication No. 42215/1983 a process for producing a lightweight heat insulating material by incorporating a thermosetting resin such as phenolic resin with inorganic foamed particles.
However, the conventional process for producing a phenolic resin foam by mixing a phenolic resin with perlite, vermiculite, obsidian, shirasu balloon, or the like is extremely slow in foaming and curing rates. In addition, this type of foam is low in compressive strength, high in water absorption, and friable because of the poor bonding between the phenolic resin and the inorganic foamed particles.
In order to overcome the above-mentioned disadvantages of conventional phenolic resin foams, the present inventors conducted a research program, which led to the finding that it is possible to produce a foam having a high compressive strength, a low water absorption, and a minimum of friability at high foaming and curing rates, by combining a specific phenolic resin, a blowing agent, a blowing auxiliary, and inorganic foamed particles with one another.